Overlapping building warning, but why?

[dieterdreist]

I get an overlapping buildings warning here: way 1561939174
But it is not a building, it is a building:part. My guess is it may have to do with the building being a multipolygon.

[skyper]

Thanks for your report, however your ticket is incomplete and therefore not helpful in its current form.

Please add all needed information according to this list:

• The required parts of the Status Report from your JOSM.
  • Please, use Report Bug from Help menu and copy & paste.
• Describe what behaviour you expected.
• Describe what did happen instead.
• Describe if and how the issue is reproducible.
• Add any relevant information like error messages or screenshots.

To ensure that all technical relevant information is contained, create new tickets by clicking in JOSMs Main Menu on Help → Report Bug.

Remember: This is a generic notice so we don't need to write the same stuff again and again. It may only apply in parts to the specific case!

---

The Status Report is really important, e.g. are there plugins or external rule installed.
As OSM data changes it is always better to attach a small example file than just a way id.

[dieterdreist]

Relative:URL: ^/trunk
Repository:UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Last:Changed Date: 2026-09-20 21:33:09 +0200 (Sun, 20 Sep 2026)
Revision:19627
Build-Date:2026-09-21 01:30:50
URL:https://josm.openstreetmap.de/svn/trunk

Identification: JOSM/1.5 (19627 en) Mac OS X 26.6.2
OS Build number: macOS 26.6.2 (25G83)
Memory Usage: 2560 MB / 14336 MB (1205 MB allocated, but free)
Java version: 17.0.20.1+0, Homebrew, OpenJDK 64-Bit Server VM
Look and Feel: javax.swing.plaf.metal.MetalLookAndFeel
Screen: Display 1 1920x1080x32bpp@60Hz (scaling 1.00×1.00) Display 2 1920x1080x32bpp@60Hz (scaling 1.00×1.00)
Maximum Screen Size: 1920×1080
Best cursor sizes: 16×16→16×16, 32×32→32×32
System property file.encoding: UTF-8
System property sun.jnu.encoding: UTF-8
Locale info: en_IT
Numbers with default locale: 1234567890 -> 1234567890
VM arguments: [--add-exports=java.base/sun.security.action=ALL-UNNAMED, --add-exports=java.desktop/com.sun.imageio.plugins.jpeg=ALL-UNNAMED, --add-exports=java.desktop/com.sun.imageio.spi=ALL-UNNAMED, -Djosm.home=<josm.pref>, -Dsun.java2d.opengl=true]
Dataset consistency test: No problems found

Plugins:
+ buildings_tools (36503)
+ reverter (36503)
+ undelete (36503)
+ utilsplugin2 (36503)

Tagging presets:
+ https://josm.openstreetmap.de/josmfile?page=Presets/ParkingLanes&zip=1
+ /Volumes/WD750/projects_wd/fix_my_city/josm-support/presets/parkraumprojekt.xml

Map paint styles:
+ https://josm.openstreetmap.de/josmfile?page=Styles/ParkingLanes&zip=1

Last errors/warnings:
- 00021.267 W: java.io.IOException: Attribution is not loaded yet
- 00021.267 W: java.io.IOException: Attribution is not loaded yet
- 00021.267 W: java.io.IOException: Attribution is not loaded yet
- 00021.268 W: java.io.IOException: Attribution is not loaded yet
- 00021.268 W: java.io.IOException: Attribution is not loaded yet
- 00021.268 W: java.io.IOException: Attribution is not loaded yet
- 00021.268 W: java.io.IOException: Attribution is not loaded yet
- 00021.269 W: java.io.IOException: Attribution is not loaded yet
- 00021.269 W: java.io.IOException: Attribution is not loaded yet
- 03437.486 W: Unsaved changes - <html>You have unsaved changes in this editor window.<br><br>Do you want to discard these changes and reload data from layer?</html>


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[GerdP]

Can you still reproduce with the given example? I can't.
Typical reasons for the problem are rounding problems where new nodes are "on" an existing line and there is a special case with multipolygons where the used Java method may calculate an unexpected result.

[dieterdreist]

If I download the area I get no validator warning, but when I modified the building:part (unnoticably) it popped up again.

[GerdP]

Please describe exactly what you modify.

[dieterdreist]

today I cannot reproduce it. I tried adding a tag and removing it, but also moving a node back and forth, both didn't yield a problem.

[GerdP]

I think I was able to reproduce by rectifying Q the outline of the multipolygon.